1. Field of the Invention
The present invention relates to a modified Gaussian lens employed in a monitor camera or the like; and, in particular, to a modified Gaussian lens having a bright F number of about 1.8 and a ratio of focal length to image size of about 4.5.
2. Description of the Prior Art
There has conventionally been known a modified Gaussian lens of a five-group, five-element configuration in which a cemented lens positioned immediately downstream of a stop in a Gaussian lens is constituted by a single lens.
Though such a modified Gaussian lens is advantageous in that the number of lenses is cut down, so that a compactness can be attained, various kinds of aberration such as chromatic aberration are considered to be hard to correct since the lens located immediately downstream of its stop is a single lens. Therefore, the one disclosed in Japanese Unexamined Patent Publication No. 57-2013 defines lens conditions so as to attain performances which are at least as good as those of a Gaussian lens of a six-element configuration.
The prior art disclosed in the above-mentioned publication and the like aim for use as a taking lens of a single-lens reflex camera, and are not intended to be mounted to a monitor camera or the like.
Therefore, such a lens has not satisfied conditions suitable for a relatively telephoto lens mounted to a monitor camera or the like, i.e., an F number of about 1.8 and a ratio of focal length to image size of about 4.5.